External midspan packing steam supply

ABSTRACT

An external supply pipe is disclosed, for supplying steam to a mid-span packing disposed about a shaft coupling a high pressure (HP) and an intermediate pressure (IP) section of an opposed flow steam turbine. The external supply pipe is disposed on an exterior of the steam turbine casing, which allows for direct measurement of steam flow to the mid-span packing.

BACKGROUND OF THE INVENTION

The invention relates generally to steam turbines having an opposed flowhigh pressure (HP)/intermediate pressure (IP) section configuration.More particularly, the invention relates to direct measurement of flowinto the IP section.

In steam turbines having an opposed flow HP/IP section arrangement,steam typically enters near the center of the casing, and flows throughthe stages of the HP section to exhaust through a reheater. Followingreheating, the steam re-enters the casing near the center, and flows inthe opposite direction through the stages of the IP section. Afterpassing through the IP section, the steam eventually travels downstreamto the low pressure (LP) section.

The HP and IP sections are coupled by a shaft having a mid-span packingdisposed about the shaft. The mid-span packing limits leakage of steamfrom the HP to the IP section, and allows the IP section to cool. Themid-span packing is wholly contained within the shell encasing the steamturbine. Accordingly, in order to quantify flow through the mid-spanpacking, it is typically inferred rather than directly measured.

A quanitification of steam volume leakage from the HP to the IP sectionis important for use in calculations evaluating performance of the steamturbine. For example, the steam leakage influences calculated efficiencyon the IP and low pressure (LP) sections of the steam turbine, and thecalculated output of all three (HP, IP, and LP) sections. One method ofinferring anticipated flow through the mid-span packing is the use of anN2 inference test. However, the N2 inference test is complicated toperform, may take one or more day to complete, requires significantcooperation from the customer and/or unit operators, and are onlycompleted on units with precision contractual tests or units that arethe subject of characterization tests. Because of these constraints, anassumed value for this flow is used on the majority of performanceanalyses. Additionally, N2 inference tests estimate the flow through themid-span packing with an associated degree of uncertainty which is solarge as to limit the usefulness of the determination.

Another method is the use of an N2 blowdown test. Like the N2 inferencetest, the N2 blowdown test requires specific turbine operatingconditions and dedicated testing time. Even with these provisions, theresults still only provide an means for estimating leakage through themid-span packing, with significant associated uncertainty.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides an opposed flow steam turbinecomprising: a high pressure (HP) section and an intermediate pressure(IP) section connected by a shaft; a mid-span packing disposed about theshaft between the HP section and the IP section; a casing disposed aboutthe steam turbine, substantially enclosing the HP section, the IPsection, the shaft, and the mid-span packing; and a supply pipe forsupplying steam to the mid-span packing, wherein the supply pipe isdisposed substantially on an exterior of the casing.

A second aspect of the disclosure provides an external supply pipe forsupplying steam to a mid-span packing of an opposed flow steam turbinehaving a casing, wherein the supply pipe is disposed substantially on anexterior of the casing.

A third aspect of the disclosure provides a method of controlling asteam flow entering an intermediate pressure (IP) section of an opposedflow configuration steam turbine, the method comprising: providing asupply pipe coupled at an upstream end to a throttle steam line, and ata downstream end to a mid-span packing, and supplying through the supplyline a known quantity of steam. The mid-span packing is disposed about ashaft coupling a high pressure (HP) section and the IP section; andprovides cooling to the IP section. The HP section is substantiallysealed. The supply pipe is disposed substantially on an exterior of acasing enclosing the steam turbine.

These and other aspects, advantages and salient features of theinvention will become apparent from the following detailed description,which, when taken in conjunction with the annexed drawings, where likeparts are designated by like reference characters throughout thedrawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an opposed flow steam turbine.

FIG. 2 shows a schematic diagram of an opposed flow steam turbine inaccordance with an embodiment of the disclosure.

FIG. 3 shows a schematic diagram of a portion of the opposed flow steamturbine of FIG. 2, in accordance with an embodiment of the disclosure.

FIG. 4 shows a schematic diagram of a portion of the opposed flow steamturbine of FIGS. 2-3, in accordance with an embodiment of thedisclosure.

It is noted that the drawings of the disclosure are not necessarily toscale. The drawings are intended to depict only typical aspects of thedisclosure, and therefore should not be considered as limiting the scopeof the disclosure. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

At least one embodiment of the present invention is described below inreference to its application in connection with the operation of a steamturbine. Although embodiments of the invention are illustrated relativeto an opposed flow HP/IP configuration steam turbine, it is understoodthat the teachings are equally applicable to steam turbines in generalhaving a packing disposed between two sections, the packing beingencased inside the casing. Further, at least one embodiment of thepresent invention is described below in reference to a nominal size andincluding a set of nominal dimensions. However, it should be apparent tothose skilled in the art that the present invention is likewiseapplicable to any suitable steam turbine. Further, it should be apparentto those skilled in the art that the present invention is likewiseapplicable to various scales of the nominal size and/or nominaldimensions.

With reference to FIG. 1, an opposed flow steam turbine 10 is described.As shown, opposed flow steam turbine 10 includes a first, or highpressure (HP) turbine section 12 operatively connected to a second,intermediate pressure (IP) turbine section 14 by a rotor or shaft 16. Amid-span packing 18 is disposed about shaft 16 between HP section 12 andIP section 14. Mid-span packing 18 may include a plurality of packingrings not individually shown in the figures, but as known in the art.Mid-span packing 18 serves to substantially prevent or limit leakage orflow of steam along shaft 16 between HP section 12 and IP section 14,and facilitates cooling of IP section 14. A shell or casing 20substantially encloses HP section 12, IP section 14, shaft 16, andmid-span packing 18, along with other features of gas turbine 10.

With continued reference to FIG. 1, in operation of steam turbine 10,high pressure, high temperature steam is delivered to HP bowl 22 bymeans of a conduit 24. Once the steam enters HP section 12, the steamflows through the stages of HP section 12 and exits HP section 12 afterthe final stage. From there, the steam is routed to reheater 26 via line28. Reheated steam is then supplied to IP bowl 30 by line 32. Steamflows through the stages of IP section 14, and exits IP section 14 vialine 34. From there it may eventually continue downstream, e.g., to alow pressure (LP) section (not shown).

During operation of the steam turbine of FIG. 1, a fraction of the hightemperature, high pressure steam flows 36 along shaft 16 within mid-spanpacking 18 and into IP section 14. This fraction of the high pressure,high temperature steam bypasses HP section 12 and reheater 26. This canimpact the overall efficiency of IP section 14, subsequent downstreamsections, and various measures of performance of steam turbine 10 as awhole.

As shown in FIGS. 2-4, according to embodiments of the disclosure, steamturbine 10 may additionally be provided with a supply pipe 40 forsupplying steam to mid-span packing 18. Supply pipe 40 is disposedsubstantially on an exterior of casing 20, such that it is accessiblefrom an exterior of steam turbine 10 without disassembly. Supply pipe 40may be connected at an upsteam end 42 to throttle steam line 44, and atdownstream end 46 to mid-span packing 18.

As shown in FIGS. 3-4, supply pipe 40 may further include a controlvalve 48 for setting a desired flow rate, and therefore the volume, ofsteam delivered to mid-span packing 18 through supply pipe 40. As shownin FIG. 4, supply pipe 40 may additionally include a flanged orifice 52,which may include at least one pressure tap 54 on a flange 56 thereoffor measuring steam flow. Flanged orifice 52 may be downstream ofcontrol valve 48 on supply pipe 40. In further embodiments, supply pipe40 may further include a thermowell 50 for measuring a temperature on aninterior of the supply pipe 40. The temperature data obtained bythermowell 50 may be used in calculations related to the power outputand/or efficiency of steam turbine 10. In some embodiments, thermowell50 may be downstream of flanged orifice 52.

Through the use of some or all of the foregoing features, supply pipe 40may deliver steam to mid-span packing 18 at a known flow rate, and in aknown volume. This allows for direct measurement of steam flow tomid-span packing 18. The accuracy and precision of a direct measurementwill be significantly higher relative to that of inferences madethrough, e.g., an N2 inference test or an N2 blowdown test, and willhave significantly reduced uncertainties associated with themeasurements. The measured flow may be compared to designspecifications, which may be used to identify performance shortfalls innew units as well as degradation on units in service such as, e.g., achange in packing clearance in mid-span packing 18. Further, themeasured flow through supply pipe 40, together with an N2 inferencetest, may be used to determine the quantity of flow through other flowpaths, or a constant measured flow during a time period.

In addition to the foregoing supply pipe 40 and steam turbine 10including a supply pipe 40, a method is provided for controlling a steamflow entering an IP section of an opposed flow configuration steamturbine.

In an embodiment, the method includes providing a supply pipe andcoupling the supply pipe at an upstream end to a throttle steam line,and at a downstream end to a mid-span packing. The mid-span packing maybe disposed about a shaft coupling a high pressure (HP) section and theIP section of the steam turbine, and may further provide cooling to theIP section.

The method may further comprise supplying steam through the supply line,and particularly, may include supplying steam through the supply pipe ata known rate and a known volume. The supply pipe may be disposedsubstantially on an exterior of a casing enclosing the steam turbine.

In one embodiment, the HP section may be substantially sealed such thatsteam may not flow out of the HP section toward the IP section, and thesteam leakage flow from the HP section to the IP section may be nominal.Further, the steam flow into the IP section may be substantiallysupplied by the supply pipe, i.e., the steam flow into the IP sectionmay substantially not be provided through leakage from the HP sectionalong the mid-span packing. In various embodiments, the known quantityof steam supplied through the supply line flows from the mid-spanpacking into the HP section and the IP section depending on a pressurein each of the respective HP and IP sections.

In some embodiments of the method, the method may include setting adesired flow rate for steam delivered through the supply pipe via acontrol valve. In further embodiments, the method may include measuringa temperature on an interior of the supply pipe using a thermowell. Instill further embodiments, the method may include providing a flangedorifice on the supply line, the flanged orifice further including atleast one pressure tap on a flange thereof. In various embodiments ofthe foregoing method, the known volume or flow rate of steam supplied tothe mid-span packing is used to determine at least one of: an HP sectionpower output, an IP section power output, an IP steam path efficiency,an LP section power output, or an LP efficiency. Because the quantity ofsteam provided to the mid-span packing via the supply pipe is known withminimal or negligible uncertainty, the amount of steam flowing into eachof the HP section and the IP section can be determined withsignificantly less uncertainty relative to calculations that arepossible based on, e.g., the N2 inference test.

As used herein, the terms “first,” “second,” and the like, do not denoteany order, quantity, or importance, but rather are used to distinguishone element from another, and the terms “a” and “an” herein do notdenote a limitation of quantity, but rather denote the presence of atleast one of the referenced item. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context (e.g., includes the degree of errorassociated with measurement of the particular quantity). The suffix“(s)” as used herein is intended to include both the singular and theplural of the term that it modifies, thereby including one or more ofthat term (e.g., the metal(s) includes one or more metals). Rangesdisclosed herein are inclusive and independently combinable (e.g.,ranges of “up to about 25 mm, or, more specifically, about 5 mm to about20 mm,” is inclusive of the endpoints and all intermediate values of theranges of “about 5 mm to about 25 mm,” etc.).

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe invention without departing from essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

What is claimed is:
 1. An opposed flow steam turbine comprising: a highpressure (HP) section and an intermediate pressure (IP) sectionconnected by a shaft; a mid-span packing disposed about the shaftbetween the HP section and the IP section; a casing disposed about thesteam turbine, substantially enclosing the HP section, the IP section,the shaft, and the mid-span packing; and a supply pipe for supplyingsteam to the mid-span packing, wherein the supply pipe is disposedsubstantially on an exterior of the casing.
 2. The opposed flow steamturbine of claim 1, wherein the supply pipe is connected at an upsteamend to a throttle steam line.
 3. The opposed flow steam turbine of claim1, wherein the supply pipe further comprises a control valve for settinga desired flow rate for steam delivered through the supply pipe.
 4. Theopposed flow steam turbine of claim 1, wherein the supply pipe furthercomprises a thermowell for measuring a temperature on an interior of thesupply pipe.
 5. The opposed flow steam turbine of claim 1, wherein thesupply pipe further comprises a flanged orifice, the flanged orificefurther including at least one pressure tap on a flange thereof.
 6. Theopposed flow steam turbine of claim 1, wherein the mid-span packinglimits a steam flow to the HP section, and provides cooling to the IPsection.
 7. The opposed flow steam turbine of claim 1, wherein thesupply pipe delivers a known quantity of steam to the mid-span packing.8. An external supply pipe for supplying steam to a mid-span packing ofan opposed flow steam turbine having a casing, wherein the supply pipeis disposed substantially on an exterior of the casing.
 9. The externalsupply pipe of claim 8, wherein the supply pipe further comprises acontrol valve for setting a desired flow rate for steam deliveredthrough the supply pipe.
 10. The external supply pipe of claim 8,wherein the supply pipe further comprises a thermowell for measuring atemperature on an interior of the supply pipe.
 11. The external supplypipe of claim 8, wherein the supply pipe further comprises a flangedorifice, the flanged orifice further including at least one pressure tapon a flange thereof.
 12. The external supply pipe of claim 8, whereinthe supply pipe delivers a known quantity of steam to the mid-spanpacking.
 13. A method of controlling a steam flow entering anintermediate pressure (IP) section of an opposed flow configurationsteam turbine, the method comprising: providing a supply pipe coupled atan upstream end to a throttle steam line, and at a downstream end to amid-span packing, the mid-span packing being disposed about a shaftcoupling a high pressure (HP) section and the IP section; and supplyingthrough the supply line a known quantity of steam, wherein the supplypipe is disposed substantially on an exterior of a casing enclosing thesteam turbine, and wherein the mid-span packing provides cooling to theIP section, and the HP section is substantially sealed.
 14. The methodof claim 13, wherein the leakage flow from the HP section to the IPsection is nominal.
 15. The method of claim 14, wherein the steam flowinto the IP section is substantially supplied by the supply pipe. 16.The method of claim 13, wherein the known quantity of steam suppliedthrough the supply line flows from the mid-span packing into the HPsection and the IP section depending on a pressure in each of the HPsection and the IP section.
 17. The method of claim 13, furthercomprising setting a desired flow rate for steam delivered through thesupply pipe with a control valve.
 18. The method of claim 13, furthercomprising providing a thermowell for measuring a temperature on aninterior of the supply pipe.
 19. The method of claim 13, furthercomprising providing a flanged orifice on the supply line, the flangedorifice further including at least one pressure tap on a flange thereof.20. The method of claim 13, further comprising: using the known quantityof steam supplied to the mid-span packing to determine at least one of:an HP section power output, an IP section power output, an IP steam pathefficiency, an LP section power output, or an LP efficiency.